Phosphatidic acid (PA) is a cofactor required for the full activation of several signaling pathways prominent in cancer cells; among these are Raf family members, PKC-ζ, SOS and mTOR. (Bonham et al., Lysophosphatidic acid acyltransferase-beta: a novel target for induction of tumour cell apoptosis. Expert Opin. Ther. Targets 2003, 7, 643-61; Zhao et al., Phospholipase D2-generated phosphatidic acid couples EGFR stimulation to Ras activation by Sos. Nat. Cell Biol. 2007, 9, 706-12; Zhang et al., Phosphatidic acid signaling regulation of Ras superfamily of small guanosine triphosphatases. Biochim. Biophys. Acta 2009, 1791, 850-5; Limatola et al., Phosphatidic acid activation of protein kinase C-zeta overexpressed in COS cells: comparison with other protein kinase C isotypes and other acidic lipids. Biochem. J. 1994, 304 (Pt 3), 1001-8.) Cells have three mechanisms for producing PA: the conversion of phosphatidylcholine (PC) to PA and choline by phospholipase D (PLD) (Cummings et al., Phospholipase D/phosphatidic acid signal transduction: role and physiological significance in lung. Mol. Cell Biochem. 2002, 234-235, 99-109); the phosphorylation of diacylglycerol (DAG) to form PA through the action diacylglycerol kinase (DAGK) Cai et al., Diacylglycerol kinases as sources of phosphatidic acid. Biochim. Biophys. Acta 2009, 1791, 942-8); and the conversion of lysophosphatidic acid (LPA) to PA by the addition of an acyl group on its sn-2 position by the enzyme lysophosphatidic acid acyltransferase (LPAAT) (Leung, The structure and functions of human lysophosphatidic acid acyltransferases. Front. Biosci. 2001, 6, D944-53). A great deal is known concerning the roles of PLD and DAGK and their contribution to PA signaling in cancer, but most research involving LPAAT has focused on its role in lipid metabolism and membrane biosynthesis. Of the five human isoforms of LPAAT (α, β, γ, δ, and ε), only LPAAT-α and LPAAT-β have been studied in any detail. These two enzymes share 48% amino acid homology as well as four highly-conserved lysophospholipid acyltransferase (LPLAT) domains essential to their enzymatic function (Shindou et al., Acyl-CoA:lysophospholipid acyltransferases. J. Biol. Chem. 2009, 284, 1-5). Though LPAAT-α expression appears to be ubiquitous, expression of LPAAT-β is less so, with its highest levels in adipose, liver, heart, and pancreas tissue (Hollenback et al., Substrate specificity of lysophosphatidic acid acyltransferase beta—evidence from membrane and whole cell assays. J. Lipid Res. 2006, 47, 593-604; Agarwal et al., Congenital generalized lipodystrophy: significance of triglyceride biosynthetic pathways. Trends Endocrinol. Metab. 2003, 14, 214-21). Mutation of the LPAAT-β gene has been shown to be the cause of a human general lipodystrophy syndrome known as congenital generalized lipodystrophy 1 (CGL1) or Berardinelli-Seip Syndrome, a disorder which is marked by a nearly complete lack of body fat in those affected as well as severe insulin resistance (Agarwal et al., AGPAT2 is mutated in congenital generalized lipodystrophy linked to chromosome 9q34. Nat. Genet. 2002, 31, 21-3). In addition to this role in lipid metabolism, recent literature has also pointed to a role for LPAAT-β in cancer. Overexpression of LPAAT-β has been observed in lung, breast, colon, prostate, and glioma tissue compared to normal adjacent tissue as well as in osteosarcoma cells. (Bonham et al., id; Rastegar et al., Lysophosphatidic acid acyltransferase beta (LPAATbeta) promotes the tumor growth of human osteosarcoma. PloS One 2010, 5, e14182; Springett et al., Lysophosphatidic acid acyltransferase-beta is a prognostic marker and therapeutic target in gynecologic malignancies. Cancer Res. 2005, 65, 9415-25.)
Because of its implicated role in cancer signaling through its production of PA, both biochemical and pharmacologic inhibition of LPAAT-β has been studied in increasing detail. Knockdown of LPAAT-β by siRNA and pharmacologic means has been shown to have antiproliferative effects in a variety of cancer cell lines. (Bonham et al., id.; Springett et al., id.; Hideshima et al., Antitumor activity of lysophosphatidic acid acyltransferase-beta inhibitors, a novel class of agents, in multiple myeloma. Cancer Res. 2003, 63, 8428-36; La Rosee et al., Antileukemic activity of lysophosphatidic acid acyltransferase-beta inhibitor CT32228 in chronic myelogenous leukemia sensitive and resistant to imatinib. Clin. Cancer Res. 2006, 12, 6540-6; Pagel et al., Induction of apoptosis using inhibitors of lysophosphatidic acid acyltransferase-beta and anti-CD20 monoclonal antibodies for treatment of human non-Hodgkin's lymphomas. Clin. Cancer Res. 2005, 11, 4857-66.) Recently, it was reported that knockdown of LPAAT-β by siRNA led to inhibition of both anchorage-dependent and -independent pancreatic cancer cell growth, and that this inhibition was related to the ability of LPAAT-β to regulate the mTORC-1 and -2 kinase signaling pathways (Blaskovich et al., Lysophosphatidic Acid Acyltransferase Beta regulates mTOR signaling. PloS One 2013, 8, e78632).

Previously, several LPAAT-β inhibitors have been reported, most notably, the 2-amino-4-anilino-6-arylpyrimidines 1 and its related pyridine 2 compounds show potent in vitro activity against LPAAT-β enzyme activity. (Gong et al., Synthesis and SAR of 2-arylbenzoxazoles, benzothiazoles and benzimidazoles as inhibitors of lysophosphatidic acid acyltransferase-beta. Bioorg. Med. Chem. Lett. 2004, 14, 1455-9; Hong et al., Diamino-C,N-diarylpyridine positional isomers as inhibitors of lysophosphatidic acid acyltransferase-beta. Bioorg. Med. Chem. Lett. 2005, 15, 4703-7.) Selected compounds of these pharmacophores were demonstrated to have inhibitory activity against anchorage-dependent and -independent growth of gynecological (Springett et al. id.), leukemic (La Rosee et al., id.), and multiple myeloma (Hideshima et al., id.) cancer cells. In addition, these compounds were shown to induce apoptosis and to have antitumor activity and increased survival of nude mouse human ovarian xenografts. Additionally the 2-arylbenzoxazole 3, and its related benzothiazole and benzimadazole were shown to have potent anti-enzymatic activity against LPAAT-β in vitro. (Gong et al., Synthesis, SAR, and antitumor properties of diamino-C,N-diarylpyrimidine positional isomers: inhibitors of lysophosphatidic acid acyltransferase-beta. Bioorg. Med. Chem. Lett. 2004, 14, 2303-8). Disclosed herein are thiosemicarbazone-based LPAAT-β inhibitors, identified through high throughput screening, with potent activity against LPAAT-β in vitro and having low micromolar anti-proliferative activity against pancreatic cancer cell growth.